Process of continuous carbonization



, Patented July 14, 1942 PROCESS F CONTINUOUS CARBONIZATION 0FCELLULOSIC MATERIALS Auguste Lambotte, Brussels, Belgium ApplicationDecember 5, 1939, Serial No. 307,707 In Germany July 9, 1938 2 Claims.

The present invention relates to the destructive distillation ofmaterials such as wood, peat, lignin and other cellulosic materialswhich, on being carbonized, give rise to an exothermic reaction.

The invention more particularly relates to a method of continuouslycarrying out distillation by treating wood or other material, preferablydried, in a chamberv or retort with inert gases introduced into theretort through the cooling zone, i. e. the zone in which the carbonizedmaterial is cooled before it is discharged from the retort. Hitherto adisadvantage of this method was the slow progress of carbonization,which could not be remedied by increasing the rate of flow of the inertgases, as said gases require to be heated in the cooling zone, and anyincrease in their rate of flow would result in lowering theirtemperature and gradually stopping the reaction Slow carbonization onthe other hand lowers the efficiency of the process and causes thedistillation products, e. g. methanol and acetic acid, to remain toolong in the carbonizing zone at a high temperature which favors theirdecomposition, thereby decreasing the yield in valuable distillationproducts. Furthermore the gases issuing at a slow rate from the coolingzone are not evenly distributed through the material, and the dischargedcharcoal is incompletely carbonized.

It is an object of my invention to avoid these disadvantages and toprovide a process in which carbonization is accelerated, while a highyield in distillation products is obtained.

In accordance with my invention the wood or other material to becarbonized is fed through a furnace or retort heated by a current ofinert gases circulating through the retort in contracurrent to the wood,said gases being heated outside the retort and introduced into theretort at an` intermediate point thereof, in immediate vicinity of thecarbonizing zone. In addition, cold i. e. `unheated gases are introduced`at or near the outlet for the carbonized materialf The rates of supplyof the hot gases and of the cold gases are independently controllable sothat it is possible both to obtain an efficient cooling of the charcoaland suitably to control the carbonizing Zone.

The wood continuously charged into the retort thus can be brought by thehot gases exactly to the temperature which is necessary in order toinduce the exothermic carbonization reaction, while the cold gasesintroduced separately absorb the heat developed by the exothermicreaction,

thereby avoiding overheating of the distillation products in contactwith the material being carbonized. In this way carbonization can becarried out rapidly, as is necessary for successful continuousoperation, Owing to the possibility of controlling the gas currentsindependently of each other, carbonization can be regulated inproportion to the input and vice versa, the extent of the carbonizingzone can be regulated as desired.

In the accompanying drawing illustrating diagrammatically, by way ofexample, a plant for carrying out the present invention, a isthecarbonizing furnace or retort having at the top an inlet chamber b forthe pieces of wood to be carbonized and at the bottom a discharge outletc for the charcoal. In operation hot inert gases are introduced into theretort at an intermediate point d thereof, whereas cold inert gases areintroduced at e near the bottom, and the gaseous products ofdistillation are withdrawn from the top at f.

In one method of carrying out my improved process, the inert gases arecirculated in a closed circuit. Issuing from the outlet f in admixturewith the products of distillation they are led through a cooler g, aseparator h and a scrubber i, whence the condensed products are co1-lected at 7'. A fan k sends the residual inert gases past a tapping pipel for discharging excess gas, through a pipe m whence a portion of thegases passes through a heater n to the hot gas inlet d, while anotherportion flows through a pipe o to the cold gas inlet e. It will beunderstood that valve v1 then is fully open, valve v2 is partly open toregulate the outward ow of excess gas; valve v3 is closed while valvesv4 and v5 are partly open to regulate the supply of gases at'd and at erespectively.

In operation, the rate of progress of the wood through the retort andthe rates of flow of the hot gases fed at d and of the cold gases fed ate are so regulateduthat, when reaching point d, the downwardlytravelling wood has reached the temperature at which exothermiccarbonization is initiated. Thus, the wood passes gradually andsuccessively through a drying zone I and a torrefaction zone II whiletravelling in contracurrent to the upward flow of hot gases introducedat d and of the cooler gases introduced at e and heated in the lowerportion of the retort. Carbonization being initiated at or near thelevel d continues throughout the zone indicated at III and is followedby cooling in zone IV in which the charcoal travels in contra-current tothe upward flow of cold inert gases introduced at e.

It has been found that, as shown, the carbonization reaction extendsbeyond the inlet of the hot gases, in the direction of travel of thewood. Owing to the fact that cold gases are continuously introduced atthe bottom of the retort, the volatile distillation products which areevolved in the carbonizing zone III, i. e. beyond the point ,d ofintroduction of the hot inert gases, remain \only for a short time incontact with charcoal at high temperature, and I have ascertained thesurprising fact that said volatile products are not decomposed to anappreciable extent, even though they pass through material in the courseof carbonizing at high temperature.

The gaseous distillation products are withdrawn with the inert gases atf. When the valuable products, such as methanol, acetic acid etc. arecondensed, a certain percentage of said products remain in thecirculating gases. It is an advantage of my process that the greaterpart of the products remaining in the circulating gases are notdecomposed since, when they are again passed through the retort, onlythe gases introduced at e pass through carbonized material liable tofavor their decomposition.

The temperature and the quantity of inert gases to be introduced dependon the amount of wood charged, the size of the pieces of wood and thedegree of moisture of the wood. As stated, the rate of input of the woodat b and the rate of flow of both the hot gases introduced 'at d and thecool gases introduced at e are such that a well defined carbonizationzone is created in the vicinity of point d, between two zones ofgradually decreasing temperatures.

In practice, the temperature of the hot inert gases at d is about 300 to600 C., while the temperature of the cold gases at e is under 40 C. Thegases and vapors escaping from the retort at f should preferably be at atemperature high enough to ensure that no condensation of the distilledproducts will take place in the cool upper portion of the retort, Suchis normally the case when the exit gases have a temperature of at least100 C. For carbonizing 1 cubic meter of wood, there is usually requireda total amount of about 800 to 2000 cubic meters of inert gasesy ofwhich 150 to 200 cubic meters are used as cold gases.

I have found that I have full control of the carbonization when the rateof travel of the wood and the rate of flow of the hot gases are soadjusted that the zone of carbonization forms beyond the inlet of thehot gasespthe said zone then being swept only by the cooling gases.Under these conditions, by merely varying the rate of flow of thecooling gases I am enabled to control the evolution of heat. Thelocation of the exotherrnic reaction zone can easily be ascertained bytemperature tests; thus if the exothermic zone were situated above thehot gas inlet, the temperature in the retort would rise above thetemperature of the inert gases introduced at d.

For carrying out my improved process I may use retorts or furnaces ofany suitable construction. Preferably I use a vertical retort as shownin the accompanying drawing in which the wood travels downwardly bygravity, the hot inert gases being introduced near or beneath the middleportion of the retort and the cool gases being introduced at the bottomnear the discharge 600 C. at a point about one fifth of the heightl ofthe retort, and 150 cubic meters of inert gases at atmospherictemperature at the bottom of the retort, near the charcoal outlet. Underthese conditions the carbonizing zone in the retort forms adjacent thelevel where the hot gases i are introduced, At the upper end of theretort the gases laden with distillation products are drawn of! at C.whereas, at the bottom, 230 kilogs. per hour of charcoal with very highcarbon content are discharged into a sealed receptacle p.

The yields in acetic acid and methanol are approximately 15 to 30%higher than those attainable with discontinuous carbonization processes.

As inert gases I may use any gases which are not adapted to react withthe distillation products, i. e. gases which are free from oxygen.Advantageously use can be made of the distillation gases formed in thecourse of the carbonization process, in which case the gases may becirculated in a closed circuit as above described.

Alternately I may use, as inert gases, natural gas where available, orproducer gas or the like, and the gases may flow in an open circuit.Fresh gas being supplied through pipe q and valve v3, a regulatedportion of said gas is sent to the retort through the heater n andanother regulated portion through the pipe o, the operation being thesame as above described. All the gases may be drawn off atl, the valvev1 being closed, or the valve v1 may be partly open, so that a portionof the inert gases is circulated through m and mixed with fresh gasesfrom q.

Whatever be the manner of circulating the gases; the heating of theinert gases introduced at d may be effected in any suitable way, as bypreheating or by combustion, i. e. the heater n may be a heat exchanger,or a furnace, or a gas producer, the heating in any case being such thatwhen entering the carbonization retort, the gases are at a temperatureof from 300 to 600 C. or even more, according to the amount of volatileproducts it is desired to allow to remain in the charcoal.

The separation of the distillation products from the circulating gasesmay be performed in the usual manner. Since, as stated before, the hotcirculating gases do not, or do only partly, come into contact with thecharcoal, it is possible to recirculate the hot distillation gaseswithout having completely separated therefrom the distillation products.Thus said products will concentrate in the gases, and if 4desired theymay be separated only in the branch circuit 0 leading the unheated gasesto the bottom of the retort, or in the branch pipe l through whichexcess gas is tapped from the circuit.

I may also introduce the heated gases at different points and atdifferent temperatures into the retort, for instance through separatecircuits. In this case less highly heated gases may be introduced intozones of lower temperature, such as the drying zone, and such gases maycontain relatively high amounts of volatile products.

The height of the temperature maximum within the retort dependsessentially on the rate of iiow and on the temperature of the hot gases.

outlet for the charcoal. With the retort 5 meters 75 The Zone 0f highesttemperature may be enlarged and its temperature lowered by suitablyincreasing the rate of flow of the hot gases.

I claim:

1. In a process of continuous carbonization of cellulosic materials inwhich heat is carefully regulated for the production of acetic acid andmethanol, passing the material to be carbonized through a chamber,introducing inert gases heated to between about 300 C. and 600 C. fromthe outside directly into said chamber at an intermediate point thereofto cause a carbonizing zone to form in said chamber in the vicinity ofsaid point, introducing inert gases at a temperature under about 40 C.into said chambernear the discharge end thereof, causing said hot andsaid cold inert gases to travel through said charnberv in contra-currentto said material, controlling. the rate of travel of said material andthe rates of flow of said hot inert gases and said cold inert gases toproduce a carbonizing zone in said retort located beyond and having itsbeginning immediately beyond the point of introduction of said hot inertgases in the direction of travel of said material, withdrawing saidinert gases from said chamber together with the acetic acid and methanolat a temperature of at least 100 C., and separating said acetic acid andmethanol from said inert gases.

2. In a process of conlinuous carbonization of cellulosic materials inwhich heat is carefully regulated for the production of acetic acid andmethanol, passing the material to be carbonized through a chamber.introducing inert gases heated to between about 300 C. and 600 C. fromthe outside directly into said chamber at an intermediate point thereofto cause a carbonizing zone to form in said chamber in the vicinity ofsaid point, introducing inert gases at a temperature under about C. intosaid chamber near the discharge end thereof, causing said hot and saidcold inert gases to travel through said chamber in contra-current tosaid material, controlling the rate of travel of said material and therates of flow of said hot inert gases and said cold inert gases toproduce a carbonizing zone in said retort located beyond and having itsbeginning immediately beyond the point of introduction of said hot inertgases in lthe direction of travel of said material, withdrawing saidinert gases from said chamber together with the acetic acid and methanolat a temperature of at least C., separating said acetic acid andmethanol from said inert gases, heating to between about 300 C.,and 600C. a portion of the separated inert gases and leading them to saidchamber as inert hot'gases, and leading another portion oi the separatedinert gases at a temperature under about 40 C. to said chamber as inertcold gases.

AUGUSTE LAMBIOTTE.

